Apparatus for the measurement of radioactivity



Sept. 11, 1951 J. HECOMOVICH APPARATUS FOR THE MEASUREMENT OFRADIOACTIVITY 7 Sheets-Sheet 1 Filed Oct. 21, 1946 //v VEN TOR JOHNHECQMOV/CH @r A TTORNEX Sept. 11, 1951 .I. HECOMOVICH APPARATUS FOR THEMEASUREMENT OF RADIOACTIVITY 7 Sheets-Sheet 2 Filed Oct. 21, 1946 /N v/vTOR do H/V HECOMOV/CH A 7'7'ORNEX (T I I I I I I I I I I I I I I I I I II I I I I I I I I I I I I I I I I I I I I I I I I I I L Sept. 11, 1951J. HECOMOVICH APPARATUS FOR THE MEASUREMENT OF RADIOACTIVITY '7Sheets-Sheet 5 Filed 001:. 21, 1946 A 7'7'ORNEK J. HECOMOVICH Sept. 11,1951 APPARATUS FOR THE MEASUREMENT OF RADIOACTIVITY 7 Sheets-Sheet 4Filed Oct. 21, 1946 //V l/E/V T01? JOHN HECOMOV/CH Sept. 11, 1951 J.HECOMOVICH APPARATUS FOR THE-MEASUREMENT OF RADIOACTIVITY 7 Sheets-Sheet5 Filed Oct. 21, 1946 JOHN HECOMO V/CH Arron/vex Sept. 11, 1951 J.HECOMOVICH 5 1 APPARATUS FOR THE MEASUREMENT OF RADIOACTIVITY Filed Oci.21, 1946 7 Sheets-Sheet e JoH/v HECOMOV/CH 0r a? E 3 hmu 3K NE uwq Sept.11, 1951 J. HECOMOVICH 2,567,568

APPARATUS FOR THE MEASUREMENT OF RADIOACTIVITY Filed Oct. 21, 1946 7Sheets-Sheet '7 CHARGE/P //v VEN TOR uoH/v HECOMOV/CH 3;

Patented Sept. 11, 1951 APPARATUS FOR THE MEASUREMENT OF RADIOACTIVITYJohn Hecomovich, San Mateo, Calif., assignor to the United States ofAmerica, as represented by the United States Atomic Energy sion Commis-Application October 21, 1946, Serial No. 704,636

6 Claims. (Cl. 250-8315) This invention relates in general to apparatusfor the measurement of radioactivity. More particularly, this inventionrelates to fission assay apparatus provided with an arrangement ofsafety devices to protect the operator from dangerous radiation and highvoltage.

, It is an object of this invention to provide ra dioactivity measuringapparatus adapted for fission assay and provided with an arrangement ofsafety devices which will protect the operator from dangerous radiationand from high voltage when using the invention.

' Other and further objects will be apparent to those skilled in the artto which it relates from the following specification, claims anddrawing.

Referring to the drawing briefly,

I Figure 1 shows a general arrangement of the assay apparatus;

I Fig. 2 shows a pulse amplifying circuit together with the associatedionization chamber employed in accordance with this invention;

Figs. 3 and 3A illustrate a bank of four discriminator networksassociated with the four ionization chambers of one lead house asemployed in accordance with this invention;

Fig. 4 is a schematic showing of the power sup- P y;

: Fig. 5 illustrates a panel for the registers and master control ofthis invention;

Fig. 6 is a view of the battery box; and

Fig. 7 is a view of the hydraulic bug elevator.

Referring to Fig. 1, there is illustrated a general arrangement of afission assay apparatus constructed in accordance with the principles ofthe present invention. Considered broadly, this apparatus includes threelead houses, house I, house 2, and house 3; three sets of discriminatornetworks, FSIA, FSZA and FS3A, and three power supplies, FSI, F82 andF83, associated with the respective lead houses; and a master controlFMC-I, The three lead houses are arranged within a cage which may beentered only through a gate controlled by a gate operator FGO-l. Thesets of discriminator networks FSI A, FS2A and FSBA, and the powersupplies FSI, FSZ and F83 and the master control FMC-l are arranged .ona common panel outside of said cage.

on which are respectively mounted four ionization chambers andassociated'amplifiers Fl, F2,

-the lead houses.

F3 and F4 of the type illustrated in Fig. 2. On the top of the roofthere is arranged a lead dome communicating with the interior of thelead house. A source of fast neutrons, known as a bug, is arranged atthe middle of each leadihouse and is arranged on a bug elevator FBL-.lat the middle of the lead house, the elevator being adapted to lower thebug into an operative position at the center of the lead house or toraise the bug into a safety position in the dome; the bug elevatorillustrated in Fig. '7 being an alternative for the pulley arrangementshown in the above-noted Segre application. The lead house issubstantially filled with parafiin or other hydrogenous substance,except for cavities therein arranged adjacent the four walls adapted tore ceive the assemblies of ionization chambers and associated amplifiersFl, F2, F3 and F4, anda central cavity into which the bug may belowered;

The output of each of the amplifiers is applied through one of theassociated discriminator'net;

works of Figs. 3 and 3A to a corresponding register (counter) 'on themaster control panel illustrated in Fig. 5.

Referring to Fig. 2, there is illustrated an ionization chamber togetherwith an associated amplifier of the type mounted on each door of At theinput of the amplifier there is illustrated an ionization chamber inwhich a sample to be analyzed is mounted. This ionization chambercomprises an electrode to which a high positive potential, for example+1000 volts, is applied through terminal I of jack J I and anotherelectrode which is connected directly to the control grid of the input.tube V5. When an atom of the sample fissions as a result of absorptionof a slow neutron, a positive pulse is applied to the grid V5, thispulse being amplified by the tubes Vi, V2, V3 and V4 and appearing as apositive pulse at terminal 6 of jack J I. This positive pulse is thenapplied through terminal 6 of jack. of Fig. 3 to the associateddiscriminator network comprising the tubes VI, V2 and V3 of Fig." 3.

The tubes VI and V2 of Fig. 3 comprise a discriminator circuit of theflip-flop type adapted to produce at its output a pulse of uniform sizeirrespective of the strength of the negative pulse applied to its inputwithin a predetermined range. This negative pulse is applied through thecoupling condenser C3 to the register drive circuit comprising tube V3,this circuit also being of the flip-flop type. Corresponding pulses aretransmitted through the output jack J3 to the terminals I and 8 of jackPGI of Fig. 5 and thence there are also switch elementsof a. manually:operable four pole shorting switch D3. When the" switch D3 is open,pulses maybe selectively applied from any ionization chamber to thecorresponding register for any selected: tim 'interval by opening thecorresponding individual short ing switches DI, D2, D and D6 for thattime interval. If the switch D3 isinitially closed and the individualswitches DI, D2, D5 and D6 are moved to their upper positions, all ofthe corresponding-registers may be operated simultaneously for the sametime interval by opening the shorting switch D3 .Ifor. that interval.Also, connected across the inputsof these four. discriminator' circuitsare normally open contacts of two timing relays. RBI and REZ which maybe energizedfor a selected. time interval by apply.- ing energy theretounder the: control of the Microfl'ex timerof Fig- 5, asmore fullydescribed hereinbelow. Theconductors connected across the windings. ofthe timing. relays REI and REZ communicate through terminals 5 and 6 ofterminal strip TS l of Fig. 3 withterminals l and 2V of jack PG3 of-Fig.5. I

Theoutputterm-inals of the amplifiers mount,- ed. on the four doors of.housel communicatelwith corresponding terminals of the selector. switchD5 of Fig. 5, through terminals 6' of. jacks J4, J6,--J9 and J] [ofFigs. 3. and 3A, and terminals 1.2,3 and-4' otterminal strip .TSI. ofFig. 3, to

terminals t, 2,-.3- andJ 4 of terminal strip .TSI of Fig.- 5. By meansof selector switch D5,the output'of any one of, the pulse amplifiersarranged on the three lead houses may be selectively applied to theinput of the cathode-ray oscilloscope 0. R. O. of Fig. 1. Thus, theoutput of any. one of the amplifiers may beexamined to determine whetherthe noiselevel of the amplifier is large enough tov rendercountinginaccurate or whether the pulse wave formissatisfactory. Thecathode-ray oscilloscope may also-be connected to the output of anyamplifier inlead house I- by connecting the oscilloscope to jack J! ofFig. 3 and selectively connecting this jack to one of these amplifiersbymeans of the selector switch D4 of Fig. 3.

Referring, to Fig. 4, there is illustrated apower supply arranged toprovide voltages to the. various, circuit elements illustratedin Figs.2, 3 and 3A associated with. lead. house I. This power supply includes ahigh voltage section and atlow voltage section in addition to thefilament supply. The low voltage section c'omprisesa negative voltagesupply comprising duo-diode V9 and a positive voltage supplyincludingduo-diode V3 and associated networks. Thehigh voltage sectioncomprises a regulatedwoltage supply comprising diode Vi, regulatedseries tube V2 and regulating shunt tube V3.

In one preferred embodiment of the inventionthe negative voltage supplyprovides a bias or -72 volts to the signal grids of the pentode sectionsof thefiip-fiop circuits comprising tubes V3, V6, VSand V12 of Figs. 3and 3A which serve drive the registers associated with lead house Inparallel with.

4 I, this bias being supplied through terminal 2 of jack J2 of Fig. 4 toterminal 2 of jack Jl of Fig. 3.

The positive voltage power supply provides:

1. A voltage of +360 volts to the flip-flop circuits including. tubesV3, V6, V9 and W2 of Figs. 3 and 3A, this voltage being applied toterminal 8 of jack J2 of Fig. 4 and terminal 8 of jack J l of Fig. 3.

2. A voltage of +255 volts to the discriminator circuits comprising. thepairs of tubes Vl--V2, V4-V5, VlV8 and Vl0Vll of Figs. 3 and 3A, thisvoltage. being applied through terminal I of jack J2 of. Fig; 4 andterminal I of jack J l of 3. A voltage of volts to the pulse amplifiersmounted on the four doors of house I; the voltage" applied-to theamplifier of Fig. 2 of the network. Fl associated with the first door,for example, being applied through terminal 3 of jack J 20f Fig. 4,terminal 3 of jack J l of Fig.3, terminal, 5 of jack J4 of Fig. 3, andterminal 5 ofJ 'ack JlofFig.-2.

Isolation networks including. four lowv pass filters comprising.inductances L4,, L5, L6 andaL'l and condensers C8, C9, CH1 and CH ofFig. 4, respectively associated therewith,are utilizedbetween thelowpositive voltage supply andthe four pulse, amplifiers associated withlead house I. to prevent pulsesoriginating in the ionization chamberassociated with any one of these amplifiers from being fed throughthepowersupply to a. counting network associated with another ionizationchamber.

,Thehigh voltage supply providesa high posh tive potential of theorder-of +1000 volts to the ionization chambers mounted in a lead houseI, this voltage being supplied through binding post BPI of Fig. 4,binding. post BPI of Fig-3 and-terminals l of jacks'J 4,. J6, J-Qand J Il ofFigs... 3 and 3A to terminal 1 of. jackJ i o,Fig.,2 of the pulseamplifier and. to corresponding terminals of. related amplifiers in leadhouse. I.. Power, is sup? plied to the input transformerTl of the. highvoltage supply through terminals l andZ otter: minal strip TS I of Fig.4. and terminals .3 andA- of jack PG3 of Fig. 5, as more fully set forthhereinbelow.. The voltage at theoutput. of the high voltage supply maybe reduced to a safe. low value when desired by closing the normallyopen contacts of. the relay REI by energizingv the winding thereof, asmore fully set forthhereinbelow. When these contacts are open, bindingpost BPI is connected directly to the relatively high valued resistor R5however, when these contacts are closed, the junction between bindingpost BPI and resistor R5 is grounded through the relatively low valuedresistor RIL. The conductors connected across thewinding of the highvoltage protective relay REI communicate through terminals 3 and 4 ofterminal strip T8! of Fig. 4 with terminals '5 and 6 of jack PG3 of Fig.5. It will be noted that the cathode andthe screen of tube. V3 .of thehigh voltage. supply are provided by the positive voltage supply of thelow voltage section.

Direct current voltage is supplied to the oathode oi the input tube V5of the pulse amplifier through jack J2 of Fig. 2, as are the input tubesof all of the amplifiers, from a common D. C. bat.- tery in the batterybox of Fig. 6. The battery may be charged at will and thus eliminate theneed of giving individual attention to batteries at the inputs of thevarious pulse amplifiers. It is important to supply the filaments of theinput tubes with D. C. current in order to reduce hum that wouldotherwise be produced if A. 0. current were utilized in this stage. Thecathodes of the remaining vacuum tubes of the pulse amplifiersassociated with lead house I and the tubes of the associated networksshown in Figs. 3 and 3A are supplied with alternating current from jackJ8 of Fig. 4.

Referring to Fig. 5, there are shown details of the master control panelFMC-l. The master control panel FMCI includes three jacks PGI, PG2 andPG4 having numerous pairs of terminals to which the outputs of theregister drives associated with the various ionization chambers of thelead houses are connected in the manner hereinabove described. Thesepairs of terminals lead to associated jacks J l, J2. J H into which anyone of the plugs PGI, PG8. PG|8 associated with the registers may beplugged. The master control panel also comprises two terminal strips TS!and TSZ communicating internally with the taps of selector switch D andexternally with the outputs of the pulse amplifiers as hereinaboveexplained. The master control FMCI also comprises a Microfiex timer andan associated control network.

Power is supplied to the master control FMC--l through the powerconnector PGB, the application of this power being under the control ofthe manually operable master switch D4. The output of this switch D4 maybe selectively impressed upon various circuits as desired through theoperate-safety switch D3; when the operate-safety stained.

2. Power is supplied to the winding of the high voltage protective relayREI of Fig. 4 discharging the condensers across the ionizationcondensers and reducing the voltage across the ionization chambers to asafe value.

3. Power is supplied to the gate operator FGOi releasing the gate andpermitting entry therethrough into the cage within which the lead housesare arranged.

It will be noted that when the operate-safety switch is in the safeposition, the cage may be entered without any danger to the operatorbeing exposed to dangerous radiation from the bug when he opens any oneof the doors. Likewise, the high voltage is removed from the ionizationchamber so that he may change samples without danger of receiving a highvoltage burn.

When the operate-safety switch D3 of Fig. 5 is moved to the left intothe operate position, power is applied to terminals 3 and 4 of jack PG3and thence to the input of the high voltage rectifier of Fig. 4, at thesame time de-energizing the solenoid of the high voltage protectiverelay REI, the solenoid of the gate operator FGO-i, and the solenoid ofthe bug elevators FBL-l, FBL--2 and FBLF-3.

The Microflex timer includes a manually adjustable timing mechanismwhich may be selectively set to time the operation thereof by means of amaster dial calibrated in minutes from 0 to 20 minutes and a vernierdial calibrated in seconds from 0 to 60 seconds. This timer includes apair of control contacts CC, these contacts being normally closed andbeing included in a circuit in series with the windings of timing relaysREI and RE! of Fig. 3. In order to time a counting operation, the startswitch DI is momentarily depressed, thus completing the circuit throughthe clutch coil and the'winding of the synchronous motor. When theclutch coil is operated, the normally open sticking contacts SC areclosed, thus causing the clutch coil and the winding 'of the synchronousmotor to remain energized when the start switch DI is opened. Also, whenthe clutch coil is energized, the control contacts'CC are opened, thusde-energizing the windings of the timing relays RE! and REZ. Uponexpiration of the predetermined time, previously manually set, theoperation of the Microflex timer is timed out and a contact (not shown)in series with the clutch coil and the winding of the synchronous motormomentarily opened, causing the contacts SC and CC to be restored totheir normal positions.

Considering now the standard procedure for operating the assayapparatus, the switch D4'is first closed and the operate-safe switch D3is set in the safe position. Under these conditions, the solenoids ofthe bug elevators FBLI, FED-2 and FBL3 are energized, thus causing thebugs in the three lead houses I, 2 and 3 to be lifted into the leaddomes at the tops of the respective lead houses and the gate to bereleased. With the bug thus elevated, the cage including the lead housesis entered, the doors of the lead houses opened and samples to beassayed introduced into the respective ionization chambers mounted onthe doors. After the doors are returned to their closed position, theoperator returns to the master control panel, and the power supplies, FSPS2, and F53, one of which is illustrated in Fig. 4, are energized byclosing switches DI and D2 of Fig. 4, thus energizing the vacuum tubesin the various pulse amplifiers and the discriminator networksassociated with the lead houses.

The operate-safe switch is then moved to the operate position, causingthe solenoids of the bug elevators to be de-energized, thus permittingthe bugs to descend into their operating positions in the interior ofthe lead houses and also the solenoid of the gate operator FGO--l to bedeenergized, thus locking the gate. Also, when the operate-safe switchis moved to the operating position, the high voltage section of thepower supply is effectively connected to the ionization chambers causinga potential of a thousand volts to be applied across each of them.Simultaneously, however, the timing relays RE'I and RE2 are energizedshorting out the inputs to the discriminator networks, thus renderingthem inoperative for actuating the various counters.

Now with the various registers plugged to circuits connected in theoutputs of the various discriminator networks and with the Microfiextimer set to time a counting operation automatically, the start buttonDi of Fig. 5 is depressed momentarily, thus initiating the operation ofthe Microflex timer, thereby opening the control contacts CC, thusde-energizing the timing relays RE! and REZ, and thus operativelyconnecting each of the pulse amplifiers to a corresponding register.With the apparatus so operating, the respective registers are actuatedeach time the corresponding ionization chamber is rendered conductivedue to the fission of an atom and the total number of such fissionswhich occur is accumulated on the respective registers. At the end ofthe time interval pre-set by the Microflex timer, the synchronous motorand clutch coil are de-energized rams to e ne isedsem a id-t s i qt vflisconn e th ls am ifie from therss et i s d ers ther b scon nu n 1hrou h the resisto s BM i ;;F. -a ith th apparatus thus rendered safe,the samples pre- "viousliv .-.ass d Ana-Y W hdr wn :i-rQ the s E iQQ Q.i atiq i chambe -an --r t. lac d by eth m samp e -it aberan s d- Th apara u i then rr dw o vus ;for-a ayin thes sa p i th m n :here n b descrb F om thefor e des ptio of h on vtion the ssay a p ratus l i een a h oa o i at al tim :n ot ctedi md n e ous m dia emittedirom th bue an i emi h lt ee- While I hav desc ib d e salien feat r eo l s v ent' n n.detai w th ;1 e "t o e --le bod. ent :it "Wil o :course =-be a parent ta num r .zinqdifi at on ma b made W t h spirit and ton o thi nve tio a,do -:notithe :eio e.:- si ilimi th in ention t t e exac detafls showexce i s fa a ethey mayebegde ined;in thefq l wi e claim What is claimed,is:

-.=1. ssay appar tus omprisin a -=eas havin a a e in on si e thereo satlo k a fi s i e ay op. tive .-assqei te withisai 0k a hav an coperate ad a sati ty posit o said :gate beinglocked when said first relay is in:its @sate y' po i i na d nlqok whe sa difirs relay is-in its operatedposition a-lead house arranged .in-said cage,,said lead -house having anopening in the wall thereof through which'a sample may be transportedand a lead-. coverifor saidopening, an auxiliary lead compartment withsaid :lead :house, a source of penetratingradiation, a movgable elementfor moving said source between an operative position in said deadhouseand a safety position in said compartment, a second relay operativelyassociated -with ;said --mo,vable element and having an operated and ;asafety position, said source ,being operatively disposed in said housewhen .said second relay is in its operated position and being disposedin said compartment when said second relay is in its safety position,and a control device located ex- ,ternally of saidlcage and operativelyassociated ,with said relays for selectively moving either of saidrelays into its operated position and the other of said relays into itssafety position.

2. Assay apparatus com-prising'a cage having a-gatein one side thereof,agate-lock, ,a first relay operatively associated with said lock andhaving an operated and a safety position, said gate being "locked whensaid first relay isin itssafety position and unlocked when said firstrelay .is in its operated position, a lead house arranged in said cage,said lead house having an opening in the-wall thereof throughwhicha-fissionable sample may :be .:-.transported rto or from -a"testposition in said house and aslead cover; for said opening, an auxiliarylead compartment communicating with said lead house, a neutron sourcecomprising a beryllium-radium mixture,: a movable element for movingsaid source betweeman and a safety-position, saidsource beingopelia-.tively-disposed in said house when ,said second relay is in itsoperated position and-being dis,-

posedin said compartment whensaidsecond relay is in its safety position,and a control device located externally oi said page and operativelyassociated with said relays for selectively mov'ng either ofsaid relaysinto its operated position and the other of said relays into its safetyposition.

3.;Assay apparatus comprisinga cage having a gate in oneiside thereof, agate look, a first ;r-elay-operatively associated with said lockandhaving an operated and asafety positiomsaid gate being locked when saidfirst-relay isi-nitssafety position and unlocked when said first relayis in its operated position, a house disposed-within said cage andhaving an assaychamber and a. communicating auxiliary chamber therein,anionization chamber arranged insaid cage within said assay chamber,said ionizationchamber having ,a pairof plates between which a sample.to .be

assayed may be mounted, a high-voltage source associated withsaid.plates, a second relay opera,-

tively associated with said high-voltagesource and having an operatedand a safety ,position,

said source being effectively connected across said plates when saidsecond relay is in itswoperated position andbeing ,efiectivelydisconnectedirdm said plates when said second relay is in its saietyposition, 3 elevator meansoperating between said assay chamber andsaidauxiliary chamber with,- in said house and adapted tocontaina,radioactive sample, a third relayhaving-an ope-ratedlpor sition and asafety position and connected vto said elevator to control thedisposition thereof,

the operated position of saidethird relay energiznectedbetweensaid-power source and-saidwelays and having a first positionmaintaining said ifirst relay in a safety position and saidsecond andthird relays in an operated position and asecond position maintainingsaid first relay in an operated position and said second and third'relays in a safety positionwhereby said gate is unlocked only when saidionization chamber is unenergized and said elevator is disposed in saidauxiliary chamber.

4. In combination, an ionization chamber hay}- ,ing .a pair oflplatesbetween which ,a sa nple to be assayed may be mounted, ahigh-voltagelpower up y a o d nser rcqnneo ed ac oss-S d pa of plates,means including ,a relatively. hi hvalued resistor connecting saidhigh-voltage source. and said ionization. chamber, and ashunting circuitincludinga relatively "low-valued re sistor and a switch connected inparallel with said condenser, whereby said condenser is quickly is d s h-"th volt aac qsssa d n a ion chamber is quickly reduced when saidswitch is closed.

5. Assay apparatus comprising an ionization chamber, a source ofpenetrating radiation movable between an operative and a retractedposition relative to said ionization chamber, first control meansoperative to move said source into said operative position from saidretracted position, a pulse counter associated With said ionizationchamber, second control means operative to disconnect said counter fromsaid ionization chamber, means for selectively operating said first andsecond control means, and means including a timer cooperating with saidsecond control means when operated for connecting said counter to saidionization chamber, for a predetermined time interval.

6. Assay apparatus comprising an ionization chamber, a source ofpenetrating radiation movable between an operative and a retractedposition relative to said ionization chamber, a first relay operative tomove said source into said retracted position when energized and intosaid operative position when de-energized, a pulse counter associatedwith said ionization chamber, a second relay adapted to effectivelydisconnect said counter from said ionization chamber when energized andto efiectively connect said counter to said ionization chamber whende-energized, master control means for selectively energizing said firstand second relays, and means including a timer for interrupting theenergization of said second relay for a predetermined time interval.JOHN HECOMOVICH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,917,108 Franke July 4, 19332,090,517 Moyer Aug. 1'7, 1937 2,232,746 Van Emden Feb. 25, 1941

1. ASSAY APPARATUS COMPRISING A CAGE HAVING A GATE IN ONE SIDE THEREOF,A GATE LOCK, A FIRST RELAY OPERATIVELY ASSOCIATED WITH SAID LOCK ANDHAVING AN OPERATED AND A SAFELY POSITION, SAID GATE BEING LOCKED WHENSAID FIRST RELAY IS IN ITS SAFETY POSITION AND UNLOCKED WHEN SAID FIRSTRELAY IS IN ITS OPERATED POSITION, A LEAD HOUSE ARRANGED IN SAID CAGE,SAID LEAD HOUSE HAVING AN OPENING IN THE WALL THEREOF THROUGH WHICH ASAMPLE MAY BE TRANSPORTED AND A LEAD COVER FOR SAID OPENING, ANAUXILIARY LEAD COMPARTMENT WITH SAID LEAD HOUSE, A SOURCE OF PENETRATINGRADIATION, A MOVABLE ELEMENT FOR MOVING SAID SOURCE BETWEEN AN OPERATIVEPOSITION IN SAID LEAD HOUSE AND A SAFETY POSITION IN SAID COMPARTMENT, ASECOND RELAY OPERATIVELY ASSOCIATED WITH SAID MOVABLE ELEMENT AND HAVINGAN OPERATED AND A SAFETY POSITION, SAID SOURCE BEING OPERATIVELYDISPOSED IN SAID HOUSE WHEN SAID SECOND RELAY IS IN ITS OPERATEDPOSITION AND BEING DISPOSED IN SAID